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55 ideas · 69 connections
Charge flow and electrical power Kirchhoff’s first law conserves charge Kirchhoff’s second law tracks energy per charge Build a resistor network from Ohm’s law A potential divider uses shared current Changing resistance makes a voltage sensor Geometry separates resistance from resistivity Power equations must use the component’s operating point Read circuit connections, not the drawing’s shape Charge and current4.1 Energy, power and resistance4.2 Charge4.1.1 Circuit symbols4.2.1 E.m.f. and potential difference4.2.2 Resistance4.2.3 Resistivity4.2.4 Power in circuits4.2.5 Series and parallel circuits4.3.1 Potential dividers4.3.3
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Build a resistor network from Ohm’s law

OCR A AS Physics · Two ideas, one explanation

Series and parallel resistance rules follow from current and voltage relationships. Redrawing a network by its junctions can make the real arrangement clear.

Series: R = ΣR Parallel: 1/R = Σ(1/R)

Follow the reasoning

  1. Identify which components share the same two junctions.
  2. Reduce one series or parallel group at a time.
  3. Use V = IR to recover the individual currents or voltages.
Specification outcomes (5)
  • 4.2.3(a) Define resistance using R = V / I and state the unit ohm.
  • 4.2.3(b) State and apply Ohm’s law.
  • 4.3.1(c) Calculate total resistance of resistors in series using R = R₁ + R₂ + …
  • 4.3.1(d) Calculate total resistance of resistors in parallel using 1/R = 1/R₁ + 1/R₂ + …
  • 4.3.1(e) Analyse circuits with components including both series and parallel arrangements.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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